1. Field of the Invention
The present invention relates to an image forming apparatus, and particularly relates to an image forming apparatus that forms an image by means of toner.
2. Description of Related Art
In an image forming apparatus, toner stored in a development unit decreases in volume under its own weight when it is left unstirred for a long period of time. When the volume of the toner decreases as thus described, a charge amount of the toner might become insufficient. It consequently becomes difficult to obtain a sufficient toner adhering amount upon forming a toner image.
As an image forming apparatus for solving the above problem, there is known, for example, an image forming apparatus described in Japanese Patent Laid-Open Publication No. H08-62984. In the image forming apparatus described in Japanese Patent Laid-Open Publication No. H08-62984, a stirring roller is rotated at a higher rate than usual when the development unit has been stopped for a predetermined time or longer. This can lead to recovery of the volume of the toner, and to recovery of the charge amount of the toner.
However, the image forming apparatus described in Japanese Patent Laid-Open Publication No. H08-62984 may stir the toner unnecessarily. More specifically, the charge amount of the toner does not depend only upon the volume of the toner. Therefore, even when the toner has been left unstirred for a long period of time and the volume of the toner has decreased, a sufficient charge amount may be obtainable. In such a case, rotating the stirring roller is not necessary. However, in the image forming apparatus described in Japanese Patent Laid-Open Publication No. H08-62984, the stirring roller is rotated on only a condition that the development unit has been stopped for a predetermined time or longer. Consequently, the image forming apparatus described in Japanese Patent Laid-Open Publication No. H08-62984 may execute unnecessary stirring.